The IXI was the world's first

digital audio player A portable media player (PMP) (also including the related digital audio player (DAP)) is a portable consumer electronics device capable of storing and playing digital media such as audio, images, and video files. The data is typically stored o ...

. It was invented by Kane Kramer in 1979. In 1981 Kramer filed for a UK patent. UK patent 2115996 was issued in 1985, and U.S. Patent 4,667,088 was issued in 1987. In 1988 Kramer's failure to raise the £60,000 required to renew the patent resulted in the patent entering the public domain, but he is still the owner of the designs. IXI was around the size of a

credit card A credit card is a payment card issued to users (cardholders) to enable the cardholder to pay a merchant for goods and services based on the cardholder's accrued debt (i.e., promise to the card issuer to pay them for the amounts plus the o ...

and had a

LCD A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but in ...

screen and navigation and volume buttons. Four prototype models were built and a pre-production model went on sale at the APRS exhibition at Earls Court in London, in October 1986.

References

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Original investor's report on the IXI from 1979 (PDF) Format
Digital audio players Portable media players Portable audio players